Optical fiber networks are increasingly common, and are standardized by international standardization committees such as American National Standards Institute (ANSI) under reference number X3T9-5. These same standards have also been adopted by the International Standards Organization (ISO). They are also included in the definition of type TPDDI networks which currently tend to be used in local area networks where the transmission distances between the various stations or terminals are relatively short.
Information messages sent by the various stations of a network consist of a plurality of frames. A frame includes data bracketed in time by signals placed at the beginning and the end of the frame, such signals being called "control characters".
In addition, the components of a computer system (processors, RAM, ROM, controller, etc.) are mounted on a set of boards of dimensions that have been standardized. These boards are usually connected to a single parallel bus for providing communication between the various elements mounted on the boards, conveying data between them, and providing electrical power.
A computer of this kind is connected to an FDDI or TPDDI network through a gateway connecting device for adapting the data transmission conditions on the computer bus to the transmission conditions on the network in question.
FIG. 1 shows the general structure of a gateway device DPC of this kind, and a computer ORD whose several component elements are mounted on a plurality of boards C communicating with one another through a bus PSB (parallel system bus). Each board C is connected to the PSB through a connecting interface IC. The type of connecting interface and the manner in which it communicates with the other functional components of the computer depend on the type of bus used. Generally the bus and connecting interface are precisely defined by standards (for example, the standards applicable to the MULTIBUS II bus, defined by standard IEEE1296).
The computer ORD is connected to a network RE in the form of a ring, of the FDDI (or TPDDI) type, for example, through a gateway connecting device DPC. Network RE includes a main ring AP and a secondary ring AS.
The gateway device DPC includes a universal coupling device GPU, a communications coupler FDI, and an interface IHA to transfer information between the GPU and the FDI.
The universal coupler GPU is connected to the PSB through a connecting interface IC, usually of the same type as the IC interfaces described above and associated with the boards C.
The gateway device DPC is physically connected to the network RE through a device DA that provides physical access to the network, associated with the communications coupler FDI.
The general structure of the device DPC as shown in FIG. 1, as well as the structure and function of the two elements GPU and FDI included in it, are described in detail in French Patent Application 89 10 156, filed Jul. 27, 1989 under the title "Gateway Device for Connecting a Computer Bus to a Fiber-Optics Ring Network"; corresponding to U.S. application Ser. No. 07/877,254, filed Apr. 28, 1992, a continuation of U.S. application Ser. No. 07/557,519, filed Jul. 24, 1990, now abandoned.
A test system can be connected to network RE by a communications coupler FDIT identical to communications coupler FDI of the gateway connecting device DPC. This is why it is useful to recall the essential components of such a communications coupler, it being understood that a more detailed description of the latter as well as its operation can be found in the French Patent Application 89 10 156, filed Jul. 27, 1989, herein incorporated by reference.
Referring to FIG. 2, the communications coupler FDI is connected to universal coupling device GPU through interface IHA, itself including an interface IHAC for the control characters and an interface IHAD for the data to be transmitted, also referred to as useful data.
Interface IHAC includes a part EC for sending the control characters and a part RC for receiving the control characters of frames coming from the network.
Interface IHAD includes a part ED for sending useful data of frames destined for the network RE and a receiving part RD adapted to receive the useful data of frames coming from the network RE.
The communications coupler FDI includes:
a transfer management controller CGT for use with a microprocessor MP associated with a group of slave elements SERV (RAM or EPROM memory, couplers, etc.) The management controller CGT is associated with a control bus BC to which elements MP, SERV, and interface IHAC are connected; PA1 a network access controller CAR, in turn connected to a device DA for physical access to the network and to control bus BC; PA1 a high-speed bus BHD (capable of carrying frames at rates on the order of 100 megabits per second), connected to interface IHAD and to network access controller CAR; and PA1 a storage memory MST connected to high-speed bus BHD and to network access controller CAR through a control line LC (including control wires for writing to and reading from the memory, as well as information for addressing the latter). PA1 traffic generation (generation of frames): this function is needed for qualification of specific devices, such as communications couplers like those shown in FIG. 2, or the wiring of such communications couplers, or the group of transmission media; PA1 display of the network: the FDDI standard provides for obtaining from any station, information on the status of the network at a given moment, including the load rate of the network, the error rate, the number of frames in circulation, etc. It is therefore useful to display on a screen the status of the network on the basis of this information; and PA1 compliance test: all FDDI-type devices must obey the standard, i.e., they must offer a given number of services. It is therefore necessary to have a tool capable of checking the existence and correct operation of such services. Among the latter are in particular the frames called SMT, defined in standard FDDI.
Now consider the transmission of a given frame from the computer ORD. After passing through universal coupling device GPU the frame arrives at the interface IHAC, in the form of useful data sent to part ED of interface IHAD, and a control block sent to part EC of interface IHAC. These control blocks include control characters relating to the content of the frame in question as well as information relating to the nature of the operations to be performed on this frame by the communications coupler FDI.
Management controller CGT reads the control blocks in interface IHAC and interprets them to form control characters in accordance with the FDDI standard relative to the frame in question. As soon as these control characters have been formed, they are sent through bus BC, controller CAR, and bus BHD to storage memory MST. During this time, the microprocessor MP manages the transfer of useful data from the frame to storage memory MST. As soon as the control characters and useful data have arrived in the memory, network access controller CAR, under the control of microprocessor MP, sends the frame thus formed to network RE.
It is clear that a process exactly opposite to that just described takes place during reception of a frame of the FDDI type coming from the network RE.
The existence of two separate buses BC and BHD for the control blocks and for the useful data, respectively, makes it possible to transfer the control blocks on bus BC independently of the corresponding useful data on bus BHD, and the control block can be transferred on its bus before, at the same time as, or after the corresponding useful data have been transferred on the bus BHD. The recent appearance of FDDI or TPDDI networks requires test tools that provided engineers or users of these networks with the following functions:
It would be desirable to provide a test system that meets the requirements listed above, and can be used with a communications coupler similar to that in FIG. 2 in which function tests are implemented (in slave elements SERV) (generation and reception of traffic . . . ) and a minicomputer of the PC type (personal computer) running specific test software. It would also be desirable for this test system to be able to drive any communications coupler connected to the network, similar to the communications coupler FDI as shown in FIG. 2, and to display the entire network on a screen of the minicomputer.